This invention relates to compatible foamable polymer blend compositions which can be formed into closed-cell foamed articles combining low density with excellent physical properties, especially stiffness, split tear, and tensile strengths.
Polymer foams find numerous uses in many types of industrial articles and consumer goods. Foams can be either elastomeric or rigid, open-cell or closed-cell, high density or low density. For certain applications such as, for example, the midsole in footwear, a readily formable, for example, by compression molding, high quality, low density foam would be very desirable; yet, a completely satisfactory material for that purpose has not yet been discovered. By "low density" is meant a density of at most about 0.15 g/cm.sup.3.
There exist commercial foamable compositions based on ethylene/vinyl acetate copolymers. Such compositions usually contain blends of ethylene/vinyl acetate copolymers with other polymers, especially with elastomers or with polyethylene, but they tend to give foams having unsatisfactory physical properties unless the foam density is at least about 0.18 g/cm.sup.3. Sometimes those prior art compositions also contain a small amount of an ionomer, such as a partially or completely neutralized copolymer of ethylene with an unsaturated carboxylic acid, which acts more or less as a compatibilizer. Although an increased proportion of ionomer would improve the foam properties, compression-molded foams of this type would be difficult to make because ionomers tend to stick to compression-molding equipment; further, ionomer foams tend to be very stiff, so that foams made from such blends would be expected to be unsatisfactory for some uses.